The timing device of the present invention has appliction to solving munition fuzing problems as well as other timing, integrating and revolution counting problems.
In recent years the fuzing for munitions such as projected grenades, 20mm., spinning bomblets and artillery has been increasing in complexity. This has been brought about by the desire for greater safety against possible malfunctions, for greater reliability to prevent dud ammunition and to increase the effectiveness of the munition against special targets. These requirements have tended to be somewhat incompatible and have increased the comlexity and the cost of munition fuzes.
The timing device of the present invention in most applications results in a dramatically simple fuze mechanism while at the same time provides for an increase in fuze safety and accuracy.
For most applications all fuze components are contained in a hermetically sealed housing which is completely filled with a low viscosity liquid. The timing device has applications primarily to spinning projectiles such as artillery, projected grenades, bomblets and gun ammunition. Through a proper choice of materials, one or more of the internal parts of the fuze is made to have approximately the same specific gravity as the fluid which surrounds it. Through this technique, the particular fuze part is relatively unaffected by rapid accelerations of the munition. Thus, in the case of an artillery fuze, for example, the projectile shortly after launch may be spinning at a high angular velocity whereas a particular part within the liquid filled fuze could have a relatively small or negligible angular velocity. This fact coupled with other mechanism permits the counting of revolutions of the projectile and arming of the fuze after a predetermined number of projectile revolutions.
Present 20mm. gun ammunition utilizes the M505 fuze which consists of a ball rotor in a spherical socket. This ball rotor has a polar moment of inertia which exceeds its transverse moments of inertia which in turn are equal. The deonator lies on the polar axis which at the time of projectile launch makes an angle of approximately 80.degree. with the spin axis of the projectile. A mathematical analysis of this fuze will show that in the absence of friction the M505 ball rotor will never align and the time required for alignment when friction is present is a function of the amount of friction and thus of the coefficient of friction, spin eccentricities, and magnitude of the projectile nutation. This has resulted in a wide variation of the arming distances of the standard M505. A typical set of firing test results for example show that some fuzes arm as early as 10 feet whereas a few fuzes require up to 100 feet. Uncontrollable sources of friction have been substantially eliminated from fuzes constructed in accordance with the teachings of this invention resulting in far more consistent arming times. In addition, the M505 does not pass current accepted safety standards for safe separation distance. Fuzes constructed in accordance with the teachings of this invention can be made with considerably longer arming distances and thus are able to satisfy the safety standards.
Other fluid timers using dashpot principles have been applied successfully to solving particular munition fuze timing problems. Most of these dashpots however, have required very tight tolerance control on the moving parts necessitating selective assembly or unusual gaging techniques. For most applications of the timing device of the present invention all of the parts can be produced on standard, high volume production metalworking machines.
In contrast to most fuzes currently produced, the timing device of the present invention is usually hermetically sealed, permitting unprotected storage in such adverse conditions as submerged under 100 feet of water. The hermetically sealed envelope is entirely filled with the damping fluid, and thus all fuze components are unaffected by rough handling or vibrations at any frequency. In addition, for many applications there is no restriction as to the location of the fuze within the munition. This feature, plus the small size, permits the use of multiple timing devices in a single munition even buried within the main explosive charge if extreme reliability is desired.
The total immersion of all fuze components in an inert liquid assures that no degradation of fuze safety of performance over prolonged storage in corrosive environments or extended exposure to severe vibrations or rough handling will take place. Rupture of the seal and loss of the liquid results in a fail safe condition.
The timing device of the present invention can in addition be used with other timing mechanisms such as disclosed in co-pending patent application, Liquid Timing Device, of D. Breed, T. Thuen and A. Breed Ser. No. 158,363, filed 6/30/71, and now abandoned.
Thus, the timing device of the present invention has been eminently successful in eliminating the drawbacks of the prior art in the field of munition fuzing.